1. Field of the Invention
The invention relates to a damper device. More particularly, the invention relates to a damper device of a lock-up clutch for use in a torque converter of a motor vehicle or the like, and to a lock-up clutch device that incorporates the damper device.
2. Description of the Related Art
Automatic transmissions are equipped with a torque converter, and are designed so that the rotation of an engine output to the crankshaft is transferred to the input shaft of a speed change device via the torque converter. Generally, the torque converter is made up of a pump impeller, a turbine runner, a stator, etc., and is equipped with a lock-up clutch device and a damper device.
Furthermore, the damper device of the lock-up clutch serves to absorb great impacts caused by sharp changes in torque at the time of lock-up engagement, and also absorbs vibrations caused by fluctuations in the torque of the engine while the vehicle is running during the locked-up clutch state.
For example, Japanese Patent Application Laid-Open Publication No. HEI 11-141617 proposes a damper device which is disposed between a clutch plate for engaging and disengaging a lock-up clutch device and an output member and which includes a spring disposed between a drive plate fixed to the clutch plate and two driven plates fixed to the output member.
Furthermore, Japanese Patent Application Laid-Open Publication No. HEI 10-47453 proposes a damper device in which strength members are reduced in size to reduce weight and reduce the size in the direction of an axis.
In the damper device disclosed in Japanese Patent Application Laid-Open Publication No. HEI 11-141617, the drive plate and the driven plates need to be rotatable relatively to each other. Therefore, it is conceivable that the drive plate and the driven plates rotatable relatively to each other are defined in position in radial directions by utilizing a portion of engagement between a groove formed in an outer peripheral edge of the drive plate and an engaging piece provided at an outer peripheral side of the clutch plate, and that the positioning of the drive plate and the driven plates, rotatable relatively to each other, in the direction of the axis is accomplished by utilizing a portion where the drive plate is sandwiched between the two driven plates via rivets.
In that case, however, the portion for positioning the drive plate and the driven plates in radial directions is located radially outward of the portion for positioning the drive and driven plates in the direction of the axis. Therefore, the damper device tends to have great dimensions in radial directions.